Method of control of electric power



Feb. 21, 1967 c. E.GE1B,JR

METHOD OF CONTROL OF ELECTRIC POWER 3 Sheets-Sheet l -Orgnal Filed Oct.17, 1962 i n I 7m. a m 4 y d, fw 7 y .p e C H 71N: f m7 ned 4 z -LA f6 Lm M d Zwin uw /b i--- w T Feb. 21, 1967 c. E. GEIB, JR 3,305,762

METHOD OF CONTROL OF ELECTRIC POWER original Filed oci. 17, 1962 3Sheetssheet 2 u u i 'f i g l INVENTOR.

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I T Ta HNF/V63 C. E. GEIB, JR

METHOD OF CONTROL OF ELECTRIC POWER Original Filed Oct. 17, 1962 Feb.21, 1967 3 Sheets-Sheet Z United States Patent() 3,365,762 METHOD OFCONTROL OF ELECTRIC POWER Carl E. Geib, Jr., Mansfield, Ohio, assignerto The Ideal Eiectric and Manufacturing Company, Mansfield, Ohio, acorporation of Ohio Original application Oct. 17, 1962, Ser.No.,231,207, now Patent No. 3,196,341. Divided and this applicationVJuly 19, 1965, Ser-.,No. 472,979v

6 Claims. (Cl. S22- 4) This is a division of my application Serial No,231,207, iiled. October 17, 1962, now Patent 3,196,341.

The present inventi-on relates to an improved method for maintaining thesupply of electrical energy to a load during all or part of theinterruption of a normal supply of electrical energy. The terminterruption is used broadly herein and includes, but is not limited to,a failure or deterioration or other undesired variation of some charLacteristic such as frequency or voltage, of a power source, or adisconnection from a power source caused .either manually orkautomatically.

The improved methods of the present invention are applicable to a widevariety of situations. In certain of these situations it is sufficientif the load in question con-A tinues after interruption of the primarysource of supply, to receive power at substantially the original voltageand frequency, for a comparatively short interval, ranging for example,from a few seconds to one orpmore minutes and then receives no furtherpower and is` shut down. In other vapplications it is desired, in theevent of interruption of the primary source of electrical energy, toactivate a standby prime -rnover such as a diesel engine. In `suchinstances, `in accordance with the present invention, the energy-storagesystem drives an electrical generator while a standby prime mover isbeing brought up to speed, and the standby prime mover thereafter drivesthe generator until the primary source of electrical energy is restored.

As compared to known power systemsso far as the present applicant isaware, and in a generic sense, a primary distinguishing characteristicof the present invention is that under normal conditions, energy isstored in an energy storage system in such quantity as to be capable ofmaintaining for a desired interval a normal rate of operation of a powersupplying element, land upon interruption of a normal supply of energythe energy storage system is caused to act as a prime mover :andgradually deliver energy to the power supplying element at such rate asto maintain substantially the normal rate of operation of the powersupplying element throughout the interval. More particularly, and asspecifically disclosed herein, energy is stored in a flywheel system bydriving such system in rotation at a rate substantially in excess of the`rate at which the aforesaid electric generator needs to be driven inorder to supply energy to the load at the desired voltage and frequency.In the event of interruption of the original source of power, theiiywheel is coupled to the generator through a precisely controlledtransmission element, preferably a clutch of the eddy current type.During the interval that power is being taken from the flywheel system,the flywheel gradually slows down from its initially higher rate ofrotation towards or to that rate of rotation (hereinafter referred tofor convenience as normal speed) needed to cause the generator todeliver power at the required voltage and frequency and during thisinterval, throughout which slippage occurs between the generator and theiiywheel system, the eddy current yclutch or other transmission elementis s controlled as to cause it to drive. the generator at the normalspeed.

The just mentioned primaryrdistinguishing feature produces manyimportant manufacturing and operating advantages. For example, dependingupon the mass of YlCC the iriywhveel system and the degree to which itshigher speed, exceeds the normal speed of the generator, the intervalthroughout which the flywheel maintains the generator at normal speedand causes the latter to continue t'o'supply the load with power atsubstantially the' normal voltage and frequency,can be varied betweenrelatively wide limits. This is of vparticular importance in thosesituations in which, in the event of interruption of a primary source ofpower a standby prime moverl such as a diesel engine is startedvandbrought up to speed and thereafter utilized, until normal service isrestored, t0 drive a generator. In such situations the present systempermits the diesel engine or other prime mover to be started and broughtup to speed in normal fashion and by the use of usual starting devices,without at the same time requiring an excessively large flywheel andwithout experiencing any noticeable degradation of either the outputvoltage or frequency of the generator during the transfer interval. i

. In certain arrangements, one of which is specifically disclosedherein, the electric generator serves as the-direct source of power forthe load under normal conditions as well as under the aforesaidpower-continuing conditions. vIn other arrangements, under normalconditions, power is .delivered .directly from the prim-ary source tothe load and also drives a 'synchronous alternator as a motor, `causingit to float on theline and function as a synchronous condenser. In theselatter arrangements, in accordance with the present invention, uponinterruption of the primary sources of power, the alternator is coupledto and driven by the energy storage system, and while so driven operatesas a generator and delivers power to the load. As illustrated hereinalso, structurally separate motors "normally drive the generator andflywheel assembly, respectively, and the eddy current clutch deliverspower to the generator only in the event of an interruption of theprimary source of power. In a generic sense, the present improvementsare also applicable to other general arrangements, as will beunderstood. v

The nature and character of the preferred and other methods of theinvention will be understood from t-he followingk description read inconjunction with the accompanying drawings, rinV which:

FIGURE 1 is a diagrammatic illustration of an electric power systemvcapable of being employed in a way constituting a practice of thepresent invention;

FIG. 2 is a view and side elevation with certain of the parts shown insection, of an illustrative 'but preferred mechanical arrangement of thedynamoelectric elements utilized in the system of FIGURE 1; and,

FIGS. 3 and 4 are diagrammatic views of illustrative regulating deviceswhich may be used with the system of FIGURE 1.

Referring to FIGURES 1 and 2, an illustrative alternating currentgenerator G is mechanically connected to and driven by an alternatingcurrent drive motor DM, which, under normal conditions, and throughcircuitry hereinafter described,'receives Ipower from an alternatingcurrent source S. Generator G may be of any suitable type but isillustrated as being a synchronous alternator of the revolving eld type.As illustrated, generator G supplies, under both normal andpower-continuing conditions, a single-phase load and is consequentlyshown as provided with a single-phase stator winding 102. The field 104of generator G receives power from an exciter Ex, which may be of anysuitable type but is illustrated as being a conventional three-phasealternating current machine, the rotor winding whereof is connectedthrough conventional rectiers r to the field winding 104 of thegenerator G, .The exciter Ex has a iield winding 106 which receivespower through circuitry described below from the generator G undercontrol of a conventional voltage regulator 108.

Referring particularly to FIGURE 2, generator G and exciter Ex will berecognized as a conventional brushless unit, therotors of both machinesbeing mounted on the same shaft and rectifiers r being carried, thoughnot shown, on a support 112 which also rotates with shaft 110.

Drive motor DM may also be of any suitable type but is illustrated asbeing a conventional revolving-field synchronousmotor, the starconnected stator windings 114-, 116 and 118 whereof are arranged forconnection through circuitry, described below, to line conductors L1, L2and L3 of source S. The field winding 120 of motor DM is arranged forconnection through slip rings diagrammatically indicated at 122 andadditional rectifiers r to receive power from the source S .through thestator windings 114, 116 and 118. The circuit for field winding iscontrolled, as described below, by a iield control contactor FCTR.

Referring particularly to FIGURE 2, the rotor shaft 124 of ymotor DM isconnected through conventional couplings 126 and 128 respectively, tothe generator shaft 110 and the shaft 130 of an eddy current clutch ECC.Clutch ECC may have any of a number of well known constructions but isillustrated as having a laminated, salient pole ield structure carriedon shaft 1311 for rotation therewith, and comprising a plurality ofpoles 132 each where'- of carries a winding 134. The eld structure 132is rotatable within and relative to a drum 135. Drum 135 is illustratedas having a smooth uninterrupted cylindrical inductor portion 136, theinner surface whereof lies immediately adjacent the pole faces of thefield structure. In the preferred practice of the invention and asherein illustrated, the drum 135 also carries a massive outer ringmember 138, of suiiicient mass to enable the eddy current drum structureto serve as the flywheel of the present system. VDrum 135 is supportedon shaft 130, for rotation relative thereto, by conventional bearingassemblies 140, and is rigidly connected to a stub shaft 142 which, atitsouter end, carries a sheave 144. As will be` evident from FIGURE 2,shafts 110, 124, 130 and 142 are supported in usual bearing assembliessuch as bearing assemblies 145'. L

Under normal conditions the drum of flywheel 135 is driven iby anaccelerating and sustaining motor SM.- As shown in FIGURE v2, motor SMis stationarily carried on the housing 144 of .the eddy current clutchstructure ECC and is driven from stub shaft 142 through the aforesaidsheave 144 and belt 146i. Y

The windings 134 of eddy current clutch ECC are illustrated in FIGURBIas being connected in series with each other and as connected throughslip rings and 152 to the output terminals a and. b of a clutchregulator 154,l the structure and characteristics of which are describedin more detail below. Motor SMmay also be of any suitable type but isillustrated as being a threephase alternating current squirrel cageinduction motor, the star-connected stator windings whereof aresupplied, under control of contacts a, b and-c of a usual mechanicalcontactor SMR, from the aforesaid source S.

It will :be observed that any suitable mechanism may be utilized as ameasure of the speed and, consequently, the output frequency of thegenerator. Preferably, and as illustrated, this is accomplished byausual direct current tachometer generator mounted at the left-hand end:of the equipment as viewed in FIGURE 2, and driven from the generatorshaft 110* through a belt 162.

Similarly, any suitable arrangement Imay tbe utilized to affect thestarting and acceleration of the drive motor DM. As shown, at start,drive motor DM receives power at a reduced voltage from line conductorsL1, L2v and L3 through an auto transformer AT under control of contactsM2a, M2b, M20,l M2d and M2e of a usual starting magnetic contactor'MZ.When the motor speed approaches its rated speed, contactor M2 isde-energized and motor DM is directly connected to line conductors L1,L2 and L3 through contacts Mla, Mlb and M1c of running contactor M1.

Preferably, drive motor DM is provide-d with a squirrel cage startingwinding. As described below, field winding 121) is shorted out duringthe acceleration period and is thereafter excited under control of fieldcontrol relay FCTR.

Under normal conditions the starting and stopping of the system is undercontrol of usual start and stop buttons and 172, usual electromagneticcontrol relays .CRL CR2, CR3` and CR4, and timers T1, T2, T3, T4 and T5.Though they may be of any suitable type, timers 'F1-TS are illustratedas being .magnetic contactors or relays provided with dash pots 174which delay,` for desired adjustable intervals after energizationof thecoils thereof, the closing of the normally open contacts thereof and theopening of the normally closed contacts thereof.

The illustrated arrangement is one in which the storedenergy system isbrought into play as a result of, or as an incident to, a disconnectionof a prime mover, in this case rdrive lmotor DM, from its normal sourceof power, in this case the source S. The requirements of the illustratedembodiment are met, if after the disconnection, the generatorV Gcontinues to supply power at substantially normal voltage and frequencyto the load 10) for a desired interval, for example, l0 seconds at -fullload. In this instance no provision is made to continue operation of thegenerator at normal speed after the expiration of the just mentionedinterval. The disconnectionl of the prime mover from its normal sourceof power may occur either manually or automatically, as will beunderstood, and is illustrated herein as .being accomplished by openinga normally closed switch 180.

It is believed that the remaining electrical and mechanical details canbest be lunderstood from a description of the operation of the hereinillustrated embodiment thereof. Before proceeding with this descriptionit is noted that all electricalcontacts are shown in the positionoccupied thereby under de-energized conditions of the associatedoperating coils or solenoids. Further, switch 18'3y is shown closed,which may -be assumed to be the position occupied thereby at all timesexcept when it is desired to bring the stored energy system into play.Finally, as illustrated, the system is at rest since conductors L1, L2and L3 are disconnected from the source S at the nowopen disconnectswitch LS.

To` condition the system for normal operation, disconnect switch LS maybe closed, thereby energizing line conductors L1, L2 and L3'. Thisaction energizes the control transformer CT which, through switch 180,energizes the coil of control relay CR1 and causes it to open itscontact CR1a and close its contact CR1b. The opening of contact CR1a ispreparatory only, but closure of contact CR1b connects the secondarywinding of control transformer CT to, and energizes, the two controlbusses 132 and 134.

Tol place the system in operation, start button 1711 may be momentarilyclosed, which action completes an obvious energizing circuit for thewinding of control relay CR2 which thereupon closes its contactCRZa-b-c. Closure of contactl CRZa completes a selfholding circuit forrelay CRZ, enabling start button 1711 to be reopened without effect.Closure of contact CR2b completes an energizing circuit through nowclosed contacts CR3a and M1d for the winding of starting contactor M2,which thereupon closes its contacts MZa-b-c-aLe and opens its contactMZ. The latter contact serves only an interlock function and preventsenergization of the running contactor M1.

Closure of contacts M2b, c and d completes obvious input circuits forwindings of the auto transformer AT and winding 116 of drive motor DM,and closure of contacts M2a and M2e connects the output terminals oftransformer AT to the lstator windings 114 and 118 of drive motor DM.

Under the conditions stated, Contact b of field control relay FCTR isclosed and, c-onsequently, field winding 120 is not excited. However, asaforementioned, motor DM preferably contains a squirrel cage startingwinding and consequently, upon energization of windings 114, 116 and11S, motor DM starts and accelerates and also starts and acceleratesgenerator G, exciter Ex and the lield structure 132 of eddy currentclutch ECC. The length of the acceleration periodof course depends uponthe rating ofthe motor DM, the magnitudes of the masses involved in thecomplete rotating system, and the ratio between the input and outputvoltages of transformer AT. As an example, transformer AT might be setto produce an output voltage of from 60 to 70% of the full voltage ofsource S. As a further example, and since'substantially no load is beingsupplied by generator G, drive rnotor DM might be expect-ed to attain 95to 97% of rated speed at the just mentioned'reduced voltage.

At the expiration of an interval, adjustable as aforesaid, butsuflicient to allow completion of the accelerating operation at reducedvoltage, motor DM is disconnected from transformer AT and is directlyconnected to line conductors L1, L2 and L3. More particularly, thepreviously mentioned closure of contact CRZC of relay CRZ completed anobvious energizing circuit for the coil of the first timing relay T1,which thereupon initiated its closing action. At the expiration of thetiming period of timing relayTl, which as an example might be from to 25sec-onds, contact Tla thereof closes. This completes an obviousenergizing circuit for the coil of control relay CRS which thereuponopens its contact CRSa and closes its contacts CR3b and CR3c.

The opening of contact CR3a interrupts the previously traced energizedcircuit for the coil of starting contactor M2. which thereupon resumesthe illustrated position, restoring all contacts thereof to theillustrated position. At substantially the same time closure of contactCR3b completes an energizing circuit for the coil of the runningcontactor M1 which circuit also includes the now closed interlockedcontact M2f of the starting contactor. It will be appreciated, ofcourse, that mechanical interlocks may be used between contactors M1 andM2 as well as the illustrated electrical interlocks to insure the propersequencing and timing relation between the reopening of the startingcontactor and the energization of the running contactor.

Upon being energized, contactorMl closes its contacts Mla-b-c andreopens its contact Mld. The latter action is without effect but theformer action connects stator windings 114, 116 and 118 of m-otor DMdirectly across the line conductor L1, L2 and L3. Thus directlyconnected across the line, motor DM completes its acceleration tosubstantially its rated speed.

The closure of contact CR3c of' control relay CRS cornpletes an obviousenergizing circuit for the coil of the second timing relay T2 whichthereupon initiates its closing action. The timing of relay T2 is setfor an interval, for example 3 to 5 seconds, long enough to allowcompletion of the acceleration of motor DM to substantially its ratedspeed.

At the conclusion of its timing interval, timing relay T2 closes itscontacts T2a and TZIJ. Closure of contact T2a completes an obviousenergized circuit for the coil of the field control relay FCTR whichthereupon closes its Contact a and opens its contact b. The latteraction interrupts the initially provided short circuit around fieldwinding 120 of motor DM. Closure of contact a completes the previouslymentioned excitation circuit for winding 120 and which includes therectiiiers r. Upon being thus supplied with direct current excitation,motor DM pulls into step and operates synchronously with the source atits rated speed.

Closure of timing relay contact T2b completes an obvious energizingcircuit for timing relay T3 which provides an interval, for example 3 to5 seconds, long enough to permit motor DM to complete the abovesynchronizing action and to permit the system to stabilize itself.

Before describing the action which results from the timing out of thethird timing relay T3, it is noted that as the acceleration of thedriving motor DM and, consequently, ofthe generator G and exciter Exproceeds, the output voltage of stator winding 102 gradually rises. Thisgradually rising output voltage is impressed, through conductors 186 and188 and the now closed contacts a and b oi remote sensing relay RSRacross the input terminals a and b of the voltage regulator 108. Theoutput terminals c and d of regulator 103 are directly connected to thefield winding 106 of the exciter Ex and, consequently, during theacceleration of generator G the exciter voltage also builds upon andprogressively increases the excitation of the generator field winding104.

Regulator 108 may be of any well known and conventional type which actsto increase or decrease the excitation of exciter field winding 106 tothe degree needed to maintain the output voltage of stator winding 102at a value which corresponds to the setting of a usual potentiometerVAR. Regulator 10S thus acts in a direction to increase the outputvoltage of generator G during the accelerating period, and, oncegenerator G obtains substantially rated speed, regulator 108 is able tosuiciently influence the excitation of generator G to maintain theoutput voltage of the latter at substantially the desired value asdetermined by the setting of the adjusting element VAR of regulator 108.

Further, during the acceleration of generator G the progressivelyraising output voltage of stator winding 102 is impressed throughconductors 190 and 192 and the normally closed protective circuitbreaker CB2 across the power input terminals c and d of the clutchregulator 154. This action is without effect, since at the present stageof the starting up operation now being described, contacts CRia and CR4bare both open end, consequently, the input control terminals e and f ofregulator 154 are deenergized. Regulator 154 is of the type which underthese conditions develops no voltage between its output terminals a andb.

Following the synchronizing of the drive motor DM, the iiywheel systemis brought up to speed, in two stages. During the first stage, the fieldwindings of the eddy current clutch ECC are partially excited, enablingdrive motor DM to start and accelerate the flywheel structure 135 up tosubstantially the rated speed of drive motor DM.

More particularly, when timing relay T3 times out as aforesaid, itcloses its contacts T3a and T311. Closure of contacts T3a completes anobvious energizing circuit for the coil of control relay CR4 whichthereupon opens its contact CRla and closes its Contact CR4b. Closure ofcontact CRllb connects the control input terminals e-f of regulator 154to the generator G through conductors and 192. An exemplary arrangementfor regulator 154 is described in more detail below, but as in the caseof regulator 108 it may be of any suitable type which, upon energizationof its power and control input terminals c-d and e-f, develops an outputvoltage between its terminals a-b determined by the ratio between areference voltage which may be set by its potentiometer SAR and a signalvoltage impressed upon its input terminals g-h by the previouslymentioned tachometer generator 160.

As will be understood, the output voltage at terminals cz-b of regulator154 causes current to flow through the field winding 134 of eddy currentclutch ECC, which action causes this element to develop a torquedetermined by the magnitude of this exciting current.

In response to the development of the just mentioned torque, the drumand iiywheel structure 135 of clutch ECC starts and accelerates towardsrated speed of drive motor DM, at which speed the field structure 132 isnow being driven by drive motor DM. Preferably and in order to avoidoverloading drive motor DM during the just mentioned acceleratingoperation of drum and ywheel assembly 135 the excitation of windings 134is kept at a low value. As shown, this is done by introducing resistor200 into the circuit of windings 134. This is accomplished by thepreviously mentioned opening of contact CR4a of relay CR4.

At the expiration of an interval, for example 25 to 30 seconds, set longenough to permit the driving motor to bring the drum and flywheelstructure and the accelerating and sustaining motor SM substantially upto rated speed of the drive motor, the excitation of the eddy currentclutch is again cut off and the motor SM is energized and caused tocomplete the acceleration of the drum and flywheel assembly to its fullvalue, which might for example be 1800 r.p.m. in a system employing adrive motor and generator rated at 1200` r.p.m.

More particularly, the previously mentioned closure of contact T3b oftiming relay T3 completed an obvious energizing circuit for the windingof timing relay T4 which thereupon initiated an opening action of itscontact T4a and initiated a closing action of its contacts T4b and T4c.These timing actions are complete-d at the end of the aforementionedperiod, for example, 25 to 30 seconds. Upon being opened, contacts T4@interrupt the previously traced energizing circuit for the coil of relayCR4 which thereupon resumes the illustrated position, reclosing contactCR4a and reopening contact CR4b. The former action is preparatory onlybut the opening of contact CR4b de-energizes the control input terminalse-f of regulator 154 there-by reducing the output voltage at terminalsa-b to zero and cutting off the excitation to the win-dings 134 of theeddy current clutch ECC and reducing to zero the torque developedthereby.

Closure of contact T4b of timing relay T4 completes an obviousenergizing circuit for the winding of contactor SMR which thereuponcloses its contacts a-b-c and energizes the stator windings 202, 264 and206 of accelerating and sustaining motor SM. Under the conditions statedthe flywheel and drum assembly 134 is running freely with respect to thefield structure 132 of the eddy current ,clutch ECC and, consequently,upon being supplied with power, motor SM is enabled to accelerate thedrum and flywheel assembly 135 to the rated speedof motor SM, which asaforesaid might be 1800 r.p.m. in a system utilizing a motor-generatorunit returned at 1200 r.p.m.

Closure of timing contact T4c completes an obvious energizing circuitfor the remaining timing relay TS which thereupon initiates a closingaction of its contact T5a and an opening action of its contact TSb.Relay T5 is set `for an interval, for example 25 to 30 seconds, which islong enough to enable motor SM to bring the drum and flywheel assemblyup to the rated speed of motor SM. At the conclusion of this periodcontacts TSa close and as shown complete a circuit for a lamp SRL whichthereupon lights and indicates to the operator that the starting upoperation has been completed and that the system is in readiness tosupply the load 100. As shown, the opening of contact TSb of relayTSinterrupts a circuit for an element 2118 which if desired may bearranged to permit or produce the connection of the generator G to theload 100 or provide other signal or control functions. As illustrated,element 20S is the shunt trip coil for the main circuit breaker CB1, itbeing understood that breaker CB1 may be of any suitable Amanually orautomatically closed type, closure whereof cannot be accomplished solong as coil 208 is energized.

Continuing with the operation now being described, if it is now desiredto supply power to the load 100, breaker CB1 is closed, therebyconnecting the load terminals 210 and 212 across stator winding 102 ofgenerator G and enabling the latter to furnish electrical energy to theload 100. Closure of breaker CB1 also completes an obvious energizingcircuit for the winding of the remote sensing relay RSR which thereuponopens its normally closed contacts a-b and closes its normally openedcontacts c-d. This action, as will be understood, enables regulator 16Sto sense voltage conditions at the load and thus eliminates the elfectof line drops that may occur along the conductors interconnecting thegenerator and the load.

Closure of circuit breaker CB1 thus puts the system into what has beenreferred to herein as normal operation during which drive motor D-Mdrives generator G at its rated normal speed, for example 12100 r.p.m.,and establishes a corresponding frequency for the output of generator G.Under these conditions also, regulator 108 continually senses thevoltage at the load and adjusts the excitation of the generator fieldwinding 104 in such manner as to maintain the just mentioned voltage atsubstantially the desired normal value.

Coming now to a description of the action of the stored-energy system,in maintaining generator G in operation at its normal speed for adesired interval after interruption of the supply of power to the drivemotor DM, it may be assume-d that the initiating switch 180 is caused toopen and this action as aforesaid may occur either manually orautomati-cally.

The opening of switch 180 interrupts the energizing circuit for the coilof relay CR1 which thereupon reopens its contact CRlb and recloses itscontacts CRla. It is believed to be evident that the reopening ofcontact CRlb de-energizes the control busses 182 and 184, therebydeenergizing the windings of all then-energized control and timingrelays and of the running contactors M1 and SMR. De-energization of thecontrol and timing relays performs no function except to put theassociated circuits in readiness for the next starting up operation.De-energization of contactors M1 and SMR disconnects the drive motor DMand the accelerating and sustaining motor SM from the source S.

Substantially simultaneously with the de-energization of motors DM andSM, contact CRla of control relay CR1 completes its closure andreconnects the control input terminals e-f of regulator 154 to thegenerator G, again causing voltage to lappear between terminals a-b ofthis regulator and again exciting the windings 134 of the eddy currentclutch and causing the latter to develop a substantial torque tending tocause the drum and ywheel structure 135 and the field structure 132 torotate together. As aforesaid, the voltage at terminals a-b of regulator154 is governed by the relationship between a reference voltagedetermined by the setting of potentiometer SAR and a signal voltagedetermined by the tachometer generator 160. The reference voltage, ofcourse, corresponds to the rated or normal speed of the generator andthe signal voltage corresponds to the actual speed of the generator.

With the drum and flywheel assembly 135 operating at a speed in excessof the rated speed of the generator, any torque developed in the eddycurrent clutch ECC of course tends to accelerate generator G to a speedin excess of its normal speed. It will be understood that regulator 154is quite sensitive and that any increase in the speed of generator Gcauses the signal voltage to increase and alter the ratio between thesignal and reference voltages in such a direction as to reduce theexcitation of the eddy current windings 134. On the other hand, the loadbeing supplied by generator G imposes a substantial decelerating forceon generator G, tending to cause its speed to fall below normal speed.Any such reduction in speed of generator G causes the signal voltage oftachometer generator to reduce, thereby altering the ratio between thesignal and control voltages in such a direction as to increase theexcitation of the eddy current windings 234, which, in turn, increasesthe torque developed in this unit and tends to accelerate the generatorto a speed equal to or above its normal speed.

So long, accordingly, as the drum and flywheel assembly 135 operates ata speed in excess of the normal speed of generator G, regulator 154 actsto increase or decrease the excitation of the eddy current clutchwindings 134 and thereby maintains the speed of generator G atsubstantially its normal value. It will be understood that the timeconstants involved in the regulator and in the eddy current clutch arecomparatively short and that, consequently, the corrective changes ineddy current torque occur very rapidly. In consequence of this, thespeed of generator G remains very close to its normal speed throughoutthe decelerating period of the flywheel structure. It will be understoodalso that the length of the decelerating period depends upon the loadbeing supplied by the generator, the relative magnitudes ofthe severalrotating masses and the degree to which the initial higher speed of theflywheel structure exceeds the normal speed of the generator. In atypical case, utilizing a 30 kw. generator and a 50 H.P. drive motoroperating at 1200 r.p.m., and a flywheel system operating at 1800 r.p.m.and having at that speed a kinetic energy of 6,140,800 foot pounds, adecelerating interval at full generator load of seconds or more isreadily available.

It will be appreciated that, in the illustrated embodiment, once thespeed of the flywheel assembly falls below the rated speed of thegenerator, excitation of the eddy current clutch remains at a maximumand the entire rotating system decelerates together and ultimately comesto rest. vWhen this has occurred, and assuming that the initiatingswitch 180 has been reclosed, the system may be started up and put intonormal operation in the previously described manner andy any furtheroperation of switch 180 again produces the same action as is describedabove.

As previously mentioned, regulator 108 may be of any well knownstructure. A suitable such structure is shown in simplified diagrammaticform in FIGURE 3 in which reference characters correspond to thoseappearing in FIGURE 1.

Referring to FIGURE 3, input terminals a and b are connecte-d to theprimary winding of a transformer CTI, the secondary winding whereof isdirectly connected through a usual triode V1 to the lield winding 106 ofthe exciter. Triode V1 may be of any suitable type but is preferably ofthe gas filled, discontinuous control type known as a thyratron.

To provide a reference voltage, independent of variations in voltage atterminals a-b, conductors 186 and 188 also supply a second controltransformer CT2 the output whereof is rectified by conventionalrectifier 210 and mpressed across a usual regulating circuit comprising-a resistor 212 and a diode 214 of the glow discharge type. It will beappreciated that upon the application to it of a voltage in excess of apredetermined amount diode 214 becomes conducting. Under suchconditions, as is well known, the current passed by diode 214 varieswith the voltage impressed across it and resistor 212 `but the voltagedrop across diode 214 remains substantially constant. This substantiallyconstant voltage is applied to the input terminals e and g of theadjusting potentiometer VAR and, consequently, the potential of terminalf thereof can be set as desired by adjustment of the movable contact216.

To provide a signal voltage, continuously proportional to the voltage atterminals a-b, conductors 186 and 188 supply a third transformer CTS,the output whereof is rectified by a conventional rectifier 218.

The just mentioned reference and signal voltages are applied, in opposedrelation, between the cathode and grid of thyratron V1 which may, ofcourse, be provided with any conventional additional grid biasingcircuitry), so that the points in successive half cycles of likepolarity, at which valve V1 lbecomes conducting, and consequently 10 theaverage current conducted thereby, is governed by the relation betweenthe two opposed reference and signal voltages.

Similarly, and as previously indicated, the eddy current clutchregulator 154 may -be of any suitable well known construction. Asuitable structure is shown in simplified diagrammatic form in FIGURE 4in which reference characters correspond to those appearing in FIGURE 1.

Referring particularly to FIGURE 4 the output of generator G is appliedto input terminals c-d and e-f. Terminals c d are connected to theprimary winding of a control transformer CT4, the secondary windingwhereof is connected to the field windings 134 of the eddy currentclutch ECC through triode V2 which may be and preferably is like triodeV1. As described in connection with FIGURE 1, this circuit also includesresistor 20) and the normally closed contacts CR4b of the previouslydescribed contr-ol relay CR4.

Input terminals eef supply a control transformer CTS the output whereofis rectified and applied across the circuit comprising resistor 220 anddischarge device 222. AS in the case of FIGURE 3, discharge device 222maintains the voltage drop thereacross at a substantially uniform value,independent of variations in the output voltage of transformer CTS, andthis substantially uniform voltage is applied across terminals i-k ofthe adjusting device SAR to provide a desired adjustable referencevoltage. In this instance, the signal voltage is derived directly fromtachometer generator 160. The opposed reference and signal voltages areapplied between the cathode and grid .Of valve V2 and, as in FIGURE 3,the relationship therebetween determines the points in successive halfcycles of like polarity at which valve V2 becomes conducting.

Conventional transient Suppressors 224 are shown in each of FIGURES 3and 4 and it will be appreciated that similar and other conventionalcircuit refinements may be used as desired in the systems of FIGURES 1,3 and 4. Such refinements have been eliminated from the present drawingsin the interest of simplicity and as not being necessary to anunderstanding of the present invention.

What is claimed is:

1. The method of supplying, during the continuation of the normal supplyof electrical energy, mechanical energy to a rotatable electricalgenerator to drive that rotatable electrical generator at a preselectedrotational velocity and to a rotatable mass to drive that rotatable massat a selected rotational velocity in preparation for subsequentlydelivering mechanical energy from the mass t-o the generator upon theinterruption of the normal supply of electrical energy which comprisesthe steps of delivering mechanical energy from a limited-capacity sourceof mechanical energy to the generator substantially to accelerate thegenerator to said preselected speed, and thereafter initiating thedelivery of energy from that same limited-capacity source to saidrotatable mass to accelerate said mass.

2. The method of supplying, during the continuation of the normal supplyof electrical energy, mechanical energy to a rotatable electricalgenerator to drive that rotatable electrical generator at a preselectedrotational velocity and to a rotatable mass to drive that rotatable massat a higher effective rotational velocity in preparation forsubsequently delivering mechanical energy from the mass to the generatorupon the interruption of the normal supply of electrical energy whichcomprises the steps of delivering mechanical energy from alimited-capacity source of niechanical energy to the generator toaccelerate the generator substantially to said preselected speed,thereafter initiating the delivery of energy from that samelimitedcapacity source to said rotatable mass to accelerate said mass toan effective velocity aproximately equal to said preselected velocity,and thereafter delivering energy to accelerate said mass to said highereffective rotational velocity.

3. The method of supplying, during the continuation of the normal supplyof electrical energy, mechanical energy to a rotatable electricalgenerator to drive that rotatable electrical generator at a preselectedrotational velocity and to a rotatable mass to drive that rotatable massat a higher effective rotational velocity in preparation forsubsequently delivering mechanical energy from the mass to the generatorupon the interruption of the normal supply of electrical energy whichcomprises the steps of delivering mechanical energy from alimited-capacity source of mechanical energy to the generatorsubstantially to accelerate the generator to said preselected speed,thereafter initiating the delivery of energy from that samelimitedcapacity source to said rotatable mass to accelerate said mass toan effective velocity approximately equal to said preselected velocity,and thereafter delivering energy from a ditferent source of mechanicalenergy to accelerate said mass to said higher effective rotationalvelocity.

4. In a method of developing and supplying mechanical driving power froma rotating mass to a rotatable electrical generator to drive thegenerator for an interval at a preselected rotational speed, the stepsof applying rotational energy from a high-torque accelerating source tothe mass to rotationally accelerate the mass from rest towards arotational velocity substantially equal to the said preselectedvelocity, effectively disconnecting the mass from the high-torqueaccelerating source, and applying rotational energy from a separatelower-torque accelerating source to the mass to accelerate the mass to arotational velocity substantially greater than said preselected velocityuntil the beginning of the said interval.

5. In a method of developing and supplying mechanical driving power froma rotating mass to a rotatable electrical generator to drive thegenerator for an interval at a preselected rotational velocity, thesteps of gradually applying rotational energy from a high-torqueaccelerating source rotating substantially at a selectedrotational speedto an initially effectively stationary mass to gradually rotationallyaccelerate the mass from rest towards an effective rotational velocitysubstantially equal to said selected rotational speed, effectivelydisconnecting the mass from the high-torque accelerating source, andapplying rotational energy from a separate lower-torque acceleratingsource to the mass to accelerate said mass to a rotational velocitysubstantially greater then said preselected velocity and substantiallygreater than said selected rotational speed until the Ibeginning of thesaid interval.

6. In a method of supplying mechanical driving power from a rotatingmass to a rotatable electrical generator to drive the generator for aninterval at a preselected rotational velocity, the steps of applyingrotational energy from a high-torque accelerating source both to themass and' to a (1e-energized separate lower-torque accelerating sourceto rotationally accelerate both the mass and said lower-torqueaccelerating source from rest towards an effective rotational velocitysubstantially greater than the said preselected velocity, effectivelydisconnecting the mass and the lower-torque accelerating source from thehigh-torque accelerating source, thereafter applying rotational energyfrom the lower-torque accelerating source to the mass to maintain therotational velocity of said mass at said effective rotational velocity,and terminating the application of rotational energy to said mass fromthe lower-torque accelerating source at the commencement of saidinterval` References Cited by the Examiner UNITED STATES PATENTS2,920,211 1/1960 Gotoh 29d-4 3,178,632 4/1965 Woodson 322--4 3,196,3417/1965 Geib 322-4 JGHN F. COUCH, Primary Examiner.

LLOYD MCCOLLUM, Examiner.

W. A. BEHA, Assistant Examiner.

1. THE METHOD OF SUPPLYING, DURING THE CONTINUATION OF THE NORMAL SUPPLYOF ELECTRICAL ENERGY, MECHANICAL ENERGY TO A ROTATABLE ELECTRICALGENERATOR TO DRIVE THAT ROTATABLE ELECTRICAL GENERATOR AT A PRESELECTEDROTATIONAL VELOCITY AND TO A ROTATABLE MASS TO DRIVE THAT ROTATABLE MASSAT A SELECTED ROTATIONAL VELOCITY IN PREPARATION FOR SUBSEQUENTLYDELIVERING MECHANICAL ENERGY FROM THE MASS TO THE GENERATOR UPON THEINTERRUPTION OF THE NORMAL SUPPLY OF ELECTRICAL ENERGY WHICH COMPRISESTHE STEPS OF DELIVERING MECHANICAL ENERGY FROM A LIMITED-CAPACITY SOURCEOF MECHANICAL ENERGY TO THE GENERATOR SUBSTANTIALLY TO ACCELERATE THEGENERATOR TO SAID PRESELECTED SPEED, AND THEREAFTER INITIATING THEDELIVERY OF ENERGY FROM THAT SAME LIMITED-CAPACITY SOURCE TO SAIDROTATABLE MASS TO ACCELERATE SAID MASS.